连续退火炉中的无氧化预热炉采用（）作为燃料。
A.高炉煤气
B.焦炉煤气
C.混合煤气
参考答案：B
等差数列{an}通项公式an=27-2n，Sn为其前n项和，则Sn最大时n的值为______．
— Do you like him?
— No. He is a person who always judges ______ appearances. [ ]
A. with
B. for
C. by
D. from
